Thrust member for fluid-operated rotary aggregates

ABSTRACT

A hydraulic or pneumatic aggregate wherein an end face of the rotor defines a control gap with the annular control face of a thrust member which is movable axially in a one-piece cover of the housing and defines with the housing inner and outer annular pressure chambers wherein the fluid acts to urge the control face toward the end face of the rotor. The thrust member has a control portion which is provided with the control face and has an end face adjacent to the outer pressure chamber, an eccentric intermediate portion having an end face which is adjacent to the inner pressure chamber, a third portion which is coaxial with the control portion, and first and second passages which respectively extend between the control face and the end faces of the control portion and intermediate portion. The control face has first and second fluid pressure zones which respectively include the ends of the first and second passages, and the end faces of the control portion and second portion respectively have third and fourth fluid pressure zones. The distances between the centers of first and second zones and the axis of the control portion respectively equal or closely approximate the distances between the axis of the control portion and the centers of the third and fourth zones. This reduces the likelihood of overheating of the aggregate due to direct contact between the control face and the rotor and is achieved by appropriate selection of the diameters of the three portions of the thrust member, the eccentricity of the second portion, the outer diameter of the control face and the configurations of the ends of first and second passages in the control face.

United States Patent [191 Eickmann [111 3,850,201 [451 Nov. 26, R974 THRUST MEMBER FOR FLUID-OPERATED ROTARY AGGREGATES [76] Inventor: Karl Eickmann, 2420 Isshiki,

Hayama-machi, Kanagawa-ken, Japan [22] Filed: May 9, I973 [21] Appl. No.: 358,803

[30] Foreign Application Priority Data Thrust Balancing of Axial Piston Machines, by Shute & Turnbull, May 1963, British Hydromechanics.

Primary Examiner-William L. Freeh Assistant Examiner-Gregory Paul LaPointe Attorney, Agent, or Firm-Michael S. Striker [57] ABSTRACT A hydraulic or pneumatic aggregate wherein an end face of the rotor defines a control gap with the annular control face of a thrust member which is movable axially in a one-piece cover of the housing and defines with the housing inner and outer annular pressure chambers wherein the fluid acts to urge the control face toward the end face of the rotor. The thrust member has a control portion which is provided with the control face and has an end face adjacent to the outer pressure chamber, an eccentric intermediate portion having an end face which is adjacent to the inner pressure chamber, a third portion which is coaxial with the control portion, and first and second passages which respectively extend between the control face and the end faces of the control portion and intermediate portion. The control face has first and second fluid pressure zones which respectively include the ends of the first and second passages, and the end faces of the control portion and second portion respectively have third and fourth fluid pressure zones. The distances between the centers of first and second zones and the axis of the control portion respectively equal or closely approximate the distances between the axis of the control portion and the centers of the third and fourth zones. This reduces the likelihood of overheating of the aggregate due to direct contact be tween the control face and the rotor and is achieved by appropriate selection of the diameters of the three portions of the thrust member, the eccentricity of the second portion, the outer diameter of the control face and the configurations of the ends of first and second passages in the control face.

30 Claims, 11 Drawing Figures PATENTELNBVZBIBH 3,850,201

SHEET 10F 2 Fig. 2 Fig. I Fig.3

THRUST MEMBER FOR FLUID-OPERATED ROTARY AGGREGATES BACKGROUND OF THE INVENTION The present invention relates to improvements in hydraulic or pneumatic aggregates in the form of pumps, motors, compressors, transmissions or the like. More particularly, the invention relates to improvements in aggregates of the type disclosed in my US. Pat. No. 3,561,328 entitled Rotary Piston Machine. Still more particularly, the invention relates to improvements in the housing, rotor and especially the thrust member of a radial piston machine or the like.

My US. Pat. No. 3,561,328 discloses an aggregate wherein an end face of the rotor is adjacent to a control face provided on a thrust member which is nonrotatably mounted in the housing and is movable axially of the rotor. The end face of the rotor is provided with channels which sweep along fluid inlet and outlet ports in the control face of the thrust member. The latter has an eccentric portion which is spaced apart from the control face and is adjacent to one of two pressure chambers which are defined by the housing and the thrust member. Each pressure chamber communicates with one of the ports in the control face. The fluid in the pressure chambers urges the thrust member axially toward the end face of the rotor to thus determine the width of the control gap between the rotor and the thrust member.

A drawback of presently known aggregates of the just outlined character is that the control face of the thrust member is likely to engage the adjacent end face of the rotor in response to increasing fluid pressure and/or in response to increasing RPM of the rotor. This causes jamming, overheating and excessive wear upon the rotor and thrust member. My aforementioned US. Pat. No. 3,561,328 proposes the provision of a so-called opposition chamber which receives pressurized fluid and is intended to reduce the likelihood of actual contact between the rotor and the thrust member. It was found that such opposition chamber cannot always prevent an overheating and the resulting drawbacks, especially at high fluid pressures and at an elevated RPM of the rotor. In fact, the adjacent faces of the thrust member and rotor are likely to be heated to melting temperature. Moreover, the means for admitting pressurized fluid into the opposition chamber contributes significantly to the cost and bulk of the aggregate, and the provision of the opposition chamber necessitates the use of a reversing cylinder and piston for the thrust member. The provision of an opposition chamber necessitates the use of a relatively long thrust member with attendant increase in the bulk of the aggregate, as considered in the axial direction of the rotor. The reasons for overheating at elevated fluid pressure and/or at a high RPM of the rotor were totally unknown so that the presently known aggregates employing the aforediscussed thrust member have a rather limited utility.

SUMMARY OF THE INVENTION An object of the invention is to provide a novel and improved thrust member which can be used in hydraulic or pneumatic aggregates as a superior substitute for conventional thrust members, which is less likely to cause an overheating of and/or other damage to the aggregate, and which is simpler, less expensive and more compact than heretofore known thrust members.

Another object of the invention is to provide a thrust member which can enhance the safety, reliability and effectiveness of the aggregate and can be installed in a one-piece part of the housing.

A further object of the invention is to provide a thrust member which is less likely to allow or cause an overheating of the aggregate than heretofore known thrust members even though the aggregate need not be provided with an opposition chamber, and which necessitates only minor changes in the design of heretofore known housings for aggregates in the form of hydraulic or pneumatic pumps, motors, compressors, transmissions or the like.

An additional object of the invention is to provide a hydraulic or pneumatic aggregate, such as a rotary piston machine, which embodies the improved thrust member.

Still another object of the invention is to provide the thrust member with a novel and improved control face and with novel and improved control and eccentric portions.

The invention is embodied in a hydraulic or pneumatic aggregate, such as a rotary piston machine, which comprises a housing having a socket (this socket is preferably provided in a one-piece portion of the housing), a rotor which is mounted in the housing and has a face facing the socket and provided with several channels for the flow of a fluid, and a novel and improved thrust member or distributor which is mounted in the socket and. is movable axially of the rotor. The thrust member has a disk-shaped control portion provided with a control face which is adjacent to the face of the rotor, a cylindrical peripheral surface and a first end face facing away from the control face; a diskshaped intermediate portion which is adjacent to the first end face, which is eccentric with respect to the 7 control portion and which has a'second cylindrical peripheral surface and a second end face facing away from the control portion; and a third portion which is adjacent to the second end face, coaxial with the control portion and has a third cylindrical peripheral surface. All three peripheral surfaces are sealingly received in the housing and the latter defines with the thrust member first and second annular pressure chambers which are respectively adjacent to the first and second end faces and receive fluid which urges the control face toward the face of the rotor. The thrust member is further provided with a first passage extending between the control face and the first end face and a second passage extending between the control face and the second end face. The control face has first and second pressure fluid zones respectively including the ends of the first and second passages in the control face, and these zones respectively comprise first and second centers located at predetermined distances from the axis of the control portion. The first and second end faces respectively have third and fourth pressure fluid zones whose centers are also located at predetermined distances from the axis of the control portion.

In accordance with a feature of the invention, the diameter of the three peripheral surfaces, the eccentricity of the second portion of the thrust member, the outer diameter of the (preferably annular) control face and/or the configurations of the ends of the first and second passages in the control face are such that the distances between the axis of the control portion and the first and second centers respectively equal or closely approximate the distances between the axis of the control portion and the third and fourth centers.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved aggregate itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an axial sectional view of a thrust member which embodies the invention;

FIG. 2 is a sectional view as seen in the direction of arrows from the line IIII of FIG. 1;

FIG. 3 is a view as seen in the direction of arrows from the line III-III of FIG. 1;

FIG. 4 is a sectional view as seen in the direction of arrows from the line IV-IV of FIG. 5;

FIG. 5 is a fragmentary axial sectional view of an aggregate which embodies the thrust member of FIGS. 1 to 3;

FIG. 6 is a diagram showing the relationship between the eccentricity of the intermediate portion of the thrust member and the distances between the centers of fluid pressure zones at the control face and first and second end faces of the thrust member;

FIG. 7 shows upon the control face of another thrust member;

FIG. 8 shows the other end of the thrust member of FIG. 7;

FIG. 9 is a sectional view of a third thrust member;

FIG. 10 is an end elevational view of the thrust member of FIG. 9; and

FIG. 11 is a sectional view of a fourth thrust member.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIGS. 1 to 3, there is shown a hol low thrust member 1 which comprises a substantially disk-shaped control portion or front portion 2, an eccentric intermediate or second portion 3, and a third or limiting portion coaxial with the control portion 2. The diameter of the cylindrical peripheral surface 8 of the limiting portion 4 determines the inner diameter of an inner annular pressure chamber 10 shown in FIG. 5. The front end face 5 of the control portion 2 constitutes a control face and the rear end face 21 of the control portion 2 bounds a part of an outer annular pressure chamber 9 shown in FIG. 5. The rear end face 22 of the eccentric intermediate portion 3 bounds a part of the inner pressure chamber 10.

The control face 5 is provided with two ports constituting the front ends of two kidney-shaped passages 35, 36. The passage 35 extends between the faces 5, 21 of the control portion 2, and the passage 36 extends betweenn the control face 5 of the control portion 2 and the rear end face 22 of the eccentric portion 3.

When the thrust member 1 is properly inserted into the socket 11a of a one-piece housing member or cover 11 shown in FIG. 5, it defines with the cover 11 the aforementioned pressure chambers 9 and 10*. The cylindrical peripheral surface 6 of the control portion 2 then cooperates with a complementary internal surface of the cover 11 to seal the outer pressure chamber 9 along its radially innermost part as shown in FIG. 5. The cylindrical peripheral surface 7 of the eccentric intermediate portion 3 cooperates with a complementary internal surface of the cover 11 to seal the innermost part of the outer pressure chamber 9 from the outermost part of the inner pressure chamber 10. The cylindrical peripheral surface 8 of the limiting portion 4 cooperates with a complementary internal surface of the cover 11 to seal the innermost part of the innerpressure chamber 10.

The center of the eccentric portion 3 is located on a line 48 (shown in FIG. 1) which is parallel to the common axis 43 of the portions 2, 4. The distance I? between the line 48 and the axis 43 represents the eccentricity of the intermediate portion 3.

Each port in the control face 5, together with the surrounding portion of this control face, constitutes a socalled control or pressure fluid zone of the control face 5. One of the two control zones is subjected to high fluid pressure and the other control zone is subjected to low fluid pressure when the aggregate embodying the thrust member 1 and cover 11 is in actual use. The first control zone which includes the port forming part of the passage 35 has a pressure field center 41 (FIG. 1), and the second control zone which includes the port forming part of the passage 36 has a pressure field center 42. The centers 41, 42 are located diametrically opposite eachother with respect to the axis 43. The distances between the centers 41, 42 and the axis 43 are respectively shown at Goa and Gci. As shown in FIG. 5, the center 41 is located opposite the outer pressure chamber 9, and the center 42 is located opposite the inner pressure chamber 10. The area of the rear end face 21 of the control portion 2 equals or approximates the cross-sectional area of the outer pressure chamber 9, and the area of the rear end face 22 of the eccentric intermediate portion 3 equals or approximates the cross-sectional area of the inner pressure chamber 10. Therefore, the center 31 of the pressure zone of the end face 21 coincides with the center 41 of the first control zone of the control face 5. The distance between the center 31 and the axis 43 is shown at gco. The axis 43 further constitutes the axis of the rotor 14 in the aggregate of FIG. 5. The center 32 of the pressure zone of the end face 22 on the eccentric portion 3 coincides with the center 42; the distance between the center 32 and the axis 43 is shown at gci. The characters 0 and i in Geo. Gci', get; and gci respectively refer to outer and inner pressure chambers 9, 10. The characters Gc denote the gravity centers or the centers of fluid pressure zones in the respective control zones of the control face 5. Thecharacters gc denote the gravity centers of the pressure fields or zones of the rear end faces (21,22) of the portions 2, 3 of the thrust member 1.

FIG. 5 shows a portion of an aggregate (e.g., a hydraulic or pneumatic compressor, pump, motor or transmission) which embodies the thrustmember l. The latter extends partially into the socket 11a of the aforementioned one-piece cover 11. The socket 11a includes two concentric sections for the coaxial portions 2 and 4 of the thrust member 1 and an eccentric intermediate section for the eccentric portion 3. As mentioned before, the cover 11 has internal cylindrical surfaces which are adjacent to the external cylindrical surfaces 6, 7, 8 of the thrust member portions 2,3 and 4. The surfaces 6, 7, 8 are received in the cover 11 with minimal clearance and may but need not be provided with plastic sealing elements. The thrust member 1 is movable axially in the cover 11. As mentioned before, the inner pressure chamber is bounded by the end face 22 and cylindrical surfaces 7 and 8, and the outer pressure chamber 9 is bounded by the end face 21 and the cylindrical surfaces 6 and 7. In addition, the chambers 9 and 10 are bounded by the adjacent radial faces and cylindrical internal surfaces of the cover 11.

FIG. 5 further shows that the thrust member 1 seals the pressure chambers 9 and 10 from the rotor 14 of the aggregate, as considered in the direction of the axis 43. The outer pressure chamber 9 is connected to a first conduit 12 for pressurized fluid, and the inner pressure chamber 10 is connected with a second conduit 13 for pressurized fluid. The conduits 12, 13 are shown in the form of channels machined into the cover 11. The fluid which enters the outer chamber 9 exerts pressure against the rear end face 21 and urges the control face 5 of the control portion 2 toward the adjacent rotating end face 57 provided on the rotor 14 or on a control ring 16 which rotates with and can be said to form part of the rotor 14. The fluid which enters the inner chamber 10 exerts pressure against the end face 22 of the eccentric portion 3 and thus urges the control face 5 toward the face 57 of the rotor 14 or control ring 16.

A control gap 58 is .maintained between the face 57 of the rotor 14 or ring 16 and the control face 5 of the control portion 2. This gap can constitute a narrow clearance between the faces 5, 57 or these faces may be held in actual contact with each other. In accordance with the presently prevailing opinion in the art to which the present invention belongs, the fluid enters the control gap 58 by way of the passages 35, 36 and its pressure decreases to zero in a direction toward the inner and outer edges of the control face 5. The drop of fluid pressure in directions from the ports in the control face toward the inner and outer edges is believed to be linear or to resemble a slightly arching curve.

The rotor 14 is provided with axially parallel channels which communicate with fluid displacing chambers 17 so that the fluid can leave the channels 15 by way of the respective chambers I7. These chambers receive radially movable fluid displacing elements 18 each of which can change the effective volume of the respective chamber 17. The rotor 14 is mounted on a thrust bearing (e.g., a pressure fluid bearing or a roller thrust bearing and rotates in one or more radial antifriction bearings 19 so that its axis coincides with or is very close and parallel to the axis 43 of the portions 2,4 of the thrust member 1. The configuration of the channels 15 is shown in FIG. 4; these channels are provided in the control ring 16 and communicate with fluid displacing chambers 17 in the rotor 14 if the aggregate employs a control ring.

FIG. 1 shows that a portion of the peripheral surface 7 may extend radially outwardly beyond the edge 44 of the control face 5 but not beyond the peripheral surface 6. FIG. 2 shows that the areas of ports (edges 37,38) in the control face 5 are larger than the crosssectional areas of the remaining portions of the passages 35,36.

For calculation of the pressure fluid field in the control gap 58, it is now assumed that the fluid pressure at the ports in the control face 5 of the control portion 2 is identical all the way between the circles 77 and 78 radius is somewhat smaller than the radius of the circular outer edge 44 of the control face 5. The radius Ri of the circle 77 is somewhat greater than the radius of the inner edge of the annular control face 5. The radius R0 of the circle 78 is somewhat greater than distances between the axis 43 and the radially outermost portions of the edges 37,38 bounding the ports in the control face 5. The radius Ri of the circle 77 is slightly smaller than the distances between the axis 43 and the radially innermost portions of the edges 37,38. The exact diameters of the circles 77,78 can be readily determined by simple experimentation. Heretofore, it was believed that the circle 77 extends substantially midway between the inner edge of the control face 5 and the innermost portions of the ports (edges 37,38). It has been found that such assumption is inaccurate, especially if the control gap 58 is very narrow or when the width of this control gap is reduced to zero.

As regards the diameter of the circle 78, it was assumed heretofore that this circle extends substantially midway between the outer edge (44) of the control face 5 and the edges 37, 38 bounding the ports in the control face. Such assumption, too, has been found to be inaccurate, especially when the distance between 37,38 on the one hand and 44 on the other hand is substantial and/or when the control gap 58 is narrow or is reduced to zero. Consequently, it is considered desirable to place the ports in the control face 5 as close as possible to the outer edge 44 and as close as possible to the inner edge of the control face; for example, the distance between 37,38 and 44 may be in the range of 2-6mm or 1/20 1/5 inch. This insures that the diameters of the circles 77,78 deviate only slightly from an ideal value, i.e., the uncertainty concerning the exact location of these circles is reduced to a minimum to thus allow for a more accurate calculation of fluid pressure fields in the control gap 58. If the distance between 37,38 and 44 is very small (e.g., 2 millimeters, the circle 78 can be assumed to pass midway between 44 on the one hand 37,38 on the other hand. However, this holds true only if the just discussed distance is very small; otherwise, such assumption regarding the position of the circle 78 can lead to gross miscalculations of pressure fluid fields in the control gap 58.

As mentioned before, the fluid pressure zones including the two ports in the control face 5 and the surrounding portions of this control face include two centers 31 and 32 whose distance from the axis 43 is respectively Gco and Gci. The cross-sectional area A of the fluid pressure zone including the port forming part of the passage 35 is calculated as follows:

A512 Rf)alpha pi/4 X 360 The cross-sectional area of the fluid pressure zone including the port forming part of the passage 36 is calculated in the same way as A i.e., with the help of the equation (1).

The force F which tends to move the thrust member 1 axially and away from the rotor 14 (i.e., the pressure which acts upon the control face 5 of the control portion 2 and upon the face 57 of the control ring 16 or rotor 14) can be calculated by multiplying the result of the equation (1) with fluid prssure p in the control gap 58. Thus,

Stz Slz X p The pressure in the control gap 58 is only one of those factors which influence the reliability of the thrust member 1. It is further necessary to determine the distances Gco and Gci. These distances are calculated as follows:

CC [2(R0 Ri)/3(R0 Ri X [(sin alpha sin alphaQ/(alpha alpha The meaning of alpha will be understood by referring to FIG. 2.

If the areas of the ports in the control face 5 (see the edges 37,38 in FIG. 2) are not enlarged in accordance with the present invention, Gco equals Gci, i.e., each of these distances equals the distance Gc in the equation (3).

In order to insure that the thrust member 1 will be urged toward the rotor 14 or control disk 16 with a requisite force (but not with an excessive force), the crosssectional areas of the pressure chambers 9 and 10 preferably exceed somewhat the cross-sectional area A according to the equation (1). Satisfactory dimensioning of pressure chambers 9 and 101 can be achieved in accordance with the equation nn.- szz X f lows:

(r rm )pi/4 [(R0 Ri )alpha X pi/4 X 360] Xjb The dimensions of the inner pressure chamber 10 can be calculated as follows:

(rm ri )pi/4 [(Ro Ri alpha X pi/ft X 360] Xfl:

the values of r0, ri and rm are shown in FIG. 3. If the aggregate is to operate safely and with a high degree of efficiency, the distances gco and gci should respectively equal or closely approximate Ga) and Gci. I

Thus, the distances gcc and gci must be calculated with a high degree of accuracy. This can be achieved by resorting to the equations B1r at and 01r 0 sin a esin (CL-0) f540l:( 4rm are 6 are 6 The equations (7) and (8) are explained in detail in my copending application Ser. No. 321,853, filed Jan. 8, 1973.

Since the equations (7) and (8) cannot be readily integrated, it is advisable to proceed as follows: One forms a number of angular intervals tau and calculates for each thereof the values under the integral symbol. The thus obtained values are totalized and the sum is divided by kl, i.e., by the average value of the area of the respective pressure zone between the angular limits of an interval. For example, one can select tau to equal 10 and one can calculate between minus 5 and 185. Thus, and referring to the equation (9), the median value of the area interval can be determined by dividing with (n 1) wherein n is the number of measured intervals.

The diagram of FIG. 6 illustrates the values of 300 I and gci as a function of the eccentricity e of the portion 3. The horizonal line Gc represents the aformentioned distance beween 41 or 42 and 43.

The configuration of the thrust member 1 is ideal if the calculation of distances get and gco furnishes a value corresponding to the point where the curves of FIG. 6 inersect each other. This point is indicative of the proper eccentricity e of the portion 3. A thrust member with an eccentric portion 3 having the just discussed ideal eccentricity would prevent jamming or overheating or wear upon the faces 5, 57 and would further prevent excessive leakage through the control gap 58. However, it was found that the curves Gc, gco and gci of FIG. 6 normally do not intersect each other at a single point. In order to achieve at least substantial coincidence of the distances Ge and go, my U.S. Pat. No. 3,561,328 proposes to employ the so-called opposition chamber and to select the diameter of the outer pressure chamber in such a way that it exceeds the outer diameter of the control face of the thrust member. At the time of conception of the invention which is disclosed in my U.S. Pat. No. 3,561,328, the distances CC and gc were determined exclusively on the basis of experiments rather than by calculation. The 7 positions of the pressure fluid centers were estimated or were determined graphically, e.g., by planimetration of the pressure chambers and fluid pressure zones. Therefore, the thrust member of my U.S. Pat. No. 3,561,238 does not insure an absolutely reliable operation of the aggregate.

In accordance with another prior proposal which is disclosed in my Austrian Pat. application Ser. No. A57/72 and which followed the conception of invention disclosed in my U.S. Pat. No. 3,561,328, the aforementioned opposition chamber can be omitted if the eccentric portion of the thrust member extends in part beyond the outer edge of the control face. This was arrived at on the basis of calculations which indicated that the center of gravity of pressure fluid (gc) should be located outwardly of the center Gc so that a part of the eccentric portion necessarily projected beyond the control face of the thrust member. This necessitated the use of a two-piece cover in order to render it possible to mount the thrust member therein. Such solution was quite satisfactory as regards the construction of the thrust member; however, the assembly and manufacture of a two-piece cover greatly increase the cost (especially the initial cost) of the aggregate. Thus, at the time of my aforediscussed earlier proposal, it was not known in the art to use a one-piece cover and to thus employ a thrust member wherein the eccentric portion does not extend beyond the edge of the control face while at the same time insuring that Gc equals gc. This 'is achieved for the first time in accordance with the present invention which provides an aggregate wherein the thrust member can be installed in a one-piece cover because its eccentric portion 3 need not extend radially beyond the outer edge 44 of the control face 5. Such construction of the cover 11 and thrust member 1 contributes to the lower cost of the aggregate and is achieved by a. proper dimensioning of the aforementioned cylindrical peripheral surface 6 which seals the outer pressure chamber 9 at the radially outermost end thereof,

b. proper dimensioning of the aforementioned cylindrical peripheral surface 7 which seals the pressure chambers 9 and 10 from each other,

c. proper dimensioning of the cylindrical peripheral surface 8 which seals the inner pressure chamber 10 at the radially innermost part thereof, and

(1. special configuration of the control face 5, its ports (channels 35,36) and the diameter of its outer edge 44.

This insures that the fluid pressure zone centers 41,42 at the control face 5 and the fluid pressure zone centers 31,32 at the end faces 21,22 are respectively located on two common lines. Consequently, the dis tances G are identical with the distance gc and the intermediate portion 3 need not extend radially outwardly beyond the control face 5.

As shown in FIG. 1, the diameter of the cylindrical peripheral surface 6 at least equals but preferably exceeds the diameter of the outer edge 44 of the control face 5 on the control portion 2. in some instances, the diameter of the peripheral surface 6 can be made smaller than the diameter of the edge 44.

The feature (b) of the present invention contributes to equality of Ge and go by properly selecting the diameter of the surface 7 relative to the surfaces 6,8 and by proper selection of the eccentricity e. As explained above, the eccentricity a will be selected by calculating the distances gc for differenteccentricities. See the equations (7), (8), (9) and HO. 6.

The aforementioned feature (0) includes the selection of the diameter of the surface 8, together with the diameter of the surface 6, in such a way that the distances gc equal the distances Gc at the control face 5. Once the radii of the cylindrical peripheral surfaces 6 and 8 are determined, the radius of the peripheral surface 7 can be calculated in accordance with the equa tion The feature (d) is also important in making the distances Gc equal to the distances gc. Thus, by increasing or reducing the diameter of the outer edge 44 of the control face 5 with respect to the diameter of the pev ripheral surface 6, one can change (increase or reduce) the distances Gc between the centers 41,42 of pressure zones at the control face 5 and the axis 43. Similar results can be achieved by changing the dimensions of the channels 15 in the rotor 14 or control ring 16 and/or by changing the dimensions of the ports (passages 35,36) in the control face 5, as considered in the radial direction of the thrust member 1.

If the outline of a channel 15 deviates from round (see FIG. 4), the outer diameter of the control face 5 can be reduced to thus allow for an increase or a reduction in the distances Gc. The inner diameter of the control face 5 is then reduced accordingly.

FIG. 6 shows that the distances gen and gci vary with changes in eccentricity e of the intermediate portion 3. Also, the distance gco does not change at the same rate as the distance gci. When the line representing the distance Gc does not intersect the curves representing the distances goo and gci at the exact point where the curve gco intersects the curve gci, it is still possible in accordance with the present invention to make the distance Gc equal to gco and gci to thus enhance the reliability of the thrust member 1. This is achieved by increasing the area of the one or the other port in the control face 5. Thus, if the distance Gc of the center 41 of the zone including the port forming part of the passage 35 is less than the distance gci or gco, this port is increased radially outwardly. lnversely, the port is extended radially inwardly if the respective Gc exceeds gco or gci. Such extension of the port radially inwardly or radially outwardly brings about a change in the distance Gc. in other words, Geo need not be identical with Gci, as long as it equals gco and as long as Gci equals gci. It is clear that any widening of the ports in the control face 5 radially inwardly or outwardly should not be accompanied by changes in the configuration of channels 15 in the rotor 14 or control ring 16. ln other. words, the ports in the control face 5 should be extended radially inwardly or outwardly beyond the channels 15.

It is further within the purview of the invention to make the outer edge 44 of the control face 5 eccentric relative to the peripheral surface 6. Such eccentricity can be resorted to in order to insure that the distances G00 and Gci respectively equal the distances gco and gcz.

An important advantage of the improved thrust member 1 is that it can be installed in a one-piece portion of the housing, that its cost is lower than the cost of conventional thrust members whose dimensions must be selected on the basis of extensive experimentation rather than by resorting to simple and reliable calculations, that it contributes to greater efficiency of the aggregate, that it can be used in aggregates wherein the fluid is maintained at an elevated pressure, that it can be used in aggregates wherein the rotor rotates at a high speed, and that its useful life (together with that of the rotor) is much longer than the useful life of conventional thrust members.

The greater efficiency, reliability and longer useful life of the improved thrust member are believed to be attributable to a number of factors including the reduced axial length of the thrust member. As explained before, the thrust member of my U.S. Pat. No.

3,561,328 is quite long due to the provision of an opposition chamber which is intended to prevent jamming and overheating. A relatively long thrust member has insufficient freedom of swiveling (spherical) movement so that its control face cannot remain exactly parallel to the end face of the rotating rotor. Another factor which is believed to contribute to greater reliability and usefulness of the improved thrust member is that the distances Gco and Gci respectively equal or vary closely approximate the distances gdo and gci. In the thrust member of my US. Pat. No. 3,561,328, the provision of the opposition chamber cannot guarantee the indentity of distances Gco and gco or Gci and 301'. As a rule, the center of the zone wherein the fluid pressure is higher is located at a first distance from the rotor axis and the center of the zone wherein the fluid pressure is lower is located at a different second distance from the rotor axis. Therefore, the control face of the thrust member which is disclosed in the aforementioned patent does not float in exact parallelism with the adjacent end face of the rotor, i.e., the control face is tilted relative to the face of the rotor which often leads to localized contact between such faces with attendant overheating and melting which normally results in immediate destruction of or in substantial damage to the aggregate. It is clear that the tilting of the patented thrust member is extremely small (as determined by the accuracy of its mounting in the housing); however, even minor tilting suffices to bring about actual contact between the rotor and the thrust member will all of the aofrediscussed consequences.

The just discussed drawbacks of the patented thrust member are avoided by constructing the improved thrust member 1 in such a way that it can be received in the socket of a one-piece housing portion (cover 11), by omitting the opposition chamber (which renders it possible to reduce the length of the thrust member and to simplify the construction of the housing), and by calculating (rather than estimating) the distances Gco, Gci, gco and gci.

As shown in FIG. 5, the maximum diameter of the pressure chamber 9 may exceed the maximum diameter of the control face 5. Also, the diameter of the peripheral surface 8 may exceed the minimum diameter of the control face 5. The control face is flat, at least in the regions surrounding the ports therein. The crosssectional area of the pressure chamber 9 and/or 10 may be 55-60 percent (plus minus 10 percent of the effective area of the control face 5. FIG. 7 shows, that the high pressure equivalent area of the control mirror (control clearance) extends from the radius 52 to the radius 53. The inner radius 52 is located substantially midway between the innermost extension of the control face and the inner wall ofthe control port 3 or 36. The outer radius 53 is located substantially midway between the outer end of the control face and the outer wall of the control port 35 or 36. The inner radius of the control face is shown at 74 and the outer radius of the control face is shown at 73. Radially beyond the peripheral surface 7 of the thrust member I has a radius 75 and extends beyond the control face. The angular interval] of angle tau between the radii 52 and 53 spans an area dF 5l which can be calculated by resorting to the equations of the specification. Radius 55 corresponds the radius r of one-of the equations and the gravity or pressure centers of the control face are located at distances Gc 5 6, from the axis of the rotor and thrust member. These distances can be calculated by resorting to the equation (3).

FIG. 8 shows the distance g 59 between the pressure center of the outer chamber and the axis of the rotor as well as the distance g abetween the axis of the rotor and the inner thrust chamber. These distances can be calculated by resorting to the equation (7) or (8). For the understanding of the respective equations the integral median value radius A 61 is shown in FIG. 8; this radius be calculated by resorting to the equations which follow. The eccentricity e of the thrust member portion 3 is indicated at 57; this eccentricity is an important factor in the following equations.

FIG. 11 shows a thrust member, which does not have an end portion 4, but only a first seat portion '71 and an eccentric second seat portion 69.

Such thrust member renders it possible to omit a third seal, and one of the thrust chambers. Since such thrust member is the shortest and the simplest at a first glance, attempts were made to determine the reliability and efficiency of such thrust member for tight seal of the control mirror with little friction.

However, since the invention provides that the pressure centers gc must have the same distance from the axis of the thrust member as the distances Gc of the pressure centers of the control face thereof, it was found by utilizing the equations of this specification that such thrust member cannot be realized for efficient work without dividing it into several parts. Either the control face becomes too wide, or the seat 68 becomes bigger than the control face, so that the control body cannot be assmebled without division. Therefore, the thrust member of FIG. 11 consists of two parts, namely a front part 70, which has the control ports 36 and 35 and an end part 7-1 which has the seat portion 68 and the eccentric portion 69. Seal grooves 67 are provided for the reception of O-ring seal means. The radial inward extension of the control face is limited by the bore or recess 71a.

By utilizing the equations of the specification, it was found that very high pressure or for very high accuracy of the identity of distances of the pressure centres Ga and gci and Ge and gco, it is necessary to provide the end portion 62 (see FIG. 9) of the thrust member with a second eccentricity which is different from eccentricity of the shoulder 3.

FIGS. 5) and 10 show that the end portion 66 of the thrust member has a second eccentricity 22 63, while its shoulder or median portion 3 has a first eccentricity el 64. O-ring seals 65 may be inserted into the respective seal grooves for making a somewhat larger clearance between the thrust chamber walls and the thrust member in order that the thrust member can move a little within its seats relative to the rotary control face of the rotor of the fluid handling device.

For many practical applications in fluid handling devices operating at fluid pressures of up to about 5,000 psi the second eccentricity can be spared and the end portion 66 can be made concentric because the second eccentricity would be very small according to the calculations by resorting to the equations of the specification.

The calculations show further, that, in order to satisfy the Ge gc condition of the invention, the outer seat portion 6 of the thrust member must extend centrically beyond the outer face of the control face (outer diameter of the control face). And, further, the control face must be limited radially inward by a recess or bore 98 shown in FIG. 9. The diameter of the end portion 66 must be bigger than the inner diameter of the control face. If these conditions are met and the basic condition of the invention, namely G gc is met, then the thrust member of the invention operates efficiently for a long period of time.

In order to achieve the desirable accuracy and thereby the efficiency and reliability of the thrust member, the values gc must be calculated with a high degree of accuracy.

The high pressure zone does not develop exactly along an arc of 180 of the control area 32, but actually along 180 plus 2, gamma, wherefrom it follows that In the equation (11), gamma represents the constant value of the high pressure aquivalent area. It is to be understood, however actually gamm is not constant but changes permanently during operation of the machine, depending you, how far a respective rotor passage extends beyond the control port 35 or 36 with which it communicates at the respective time. The constant value gamma is, therefore an average value for a given period of time. Depending on the size and configuration of the control area the value of gamma is normally between 0 and With the above in mind the control area can be replaced for convenience of calculation by the high pressure aquivalent area A HPm which is determined as follows:

' ance factorjb as follows:'

wherein the balance factorjb is commonly 1,056 $0.2 depending upon, how strongly the control body shall be pressed against the rotary control face and how strong the resisting frictional forces in the seals etc. are. Actually there are seals, like O-rings, provided between the respective seats in the housing and the respective portions of the thrust member, For high pressure devices suchassumption would lead, as is recognized by this invention, again to local overstressing in one area of the control zone and to much lower pressures in the other zone of the control area because the pressure centers of the control area would not be located midway between ri and r0.

According to this ivention, the pressure center of the high pressure aquivalent area of the control area is located on the integral median value of the high pressure aquivalent area of the control area.

Thus, according to this invention, the integral median radius rgc is introduced. By considering the area portion dF 51 of FIG. 7, the integral median radius rgc is calculated as follows 07r frrdr 0 ut s However, the determination of the integral median' cos ada G v a] a1 T dor Sin (lg-Sin (X1 isatssavalsss... .1

If in this equation rgc equals 1, then a fixed courve appears over the angle area, which provides the factor fG. For the area 0 to the factor fG is 0.636.

For actual calculation of the gravity center distance Gc the value fG is to be multiplied with the Value rgc. Depending on angle gamma of equation (11) the value of fG varies between 0.4 and 0.7 for practical applications.

U.S. Pat. No. 3,320,897 discloses a method for calculating the median integral value A through a section through two circles of different radii r and R and an ec centricity 2 between the centers of both circles. However, since the inner and outer diameters of each of the pressure chambers form circles of different radii and both chambers have an eccentricity e, median value A see FIG. 8, reference character through the outer face of a sector of angle tau reference character in FIG. 8, can be used for calculating the value A of the respective pressure chamber of the invention.-

This median integral value A is calculated according to U.S. Pat. No. 3,320,897 as follows:

which reads after integration:

Therein is to the outer radius of the respective pressure chamber or thrust-body portion. The angle tau is the The next step is to calculate the cross-sectional area of the interval 57 of FIG. fl which is called Kl in accordance with U.S. Pat. No. 3,320,897 and it is calculated as follows From the values of K1 the integral median value of K1 is to be found in order to be able to calculate with the said median integral value K 1. The median value of K1 can be found by computing all calculated intervals of K1 and by dividing the thus obtained sum by the number z of the intervals. This is calculated as follows:

1?, K, /2 number of intervals.

For determining the pressure center of the respective fluid containing pressure chamber it is necessary to calculate each pressure center of each section interval K1 of the angle tau.

In this respect it is to be recognized in accordance with this invention, that the pressure center of the interval K1 is not in the middle between the inner and outer seal faces because the outer part of interval K1 is wider than its inner part. Consequently the pressure center of the interval KI is nearer to its radially outer end. It is therefore necessary to find the radius rg on which the pressure center of the respective interval K 1 is located. The radius rg is the radial integral median value through the cross-sectional area of the interval KI and is calculated as follows:

For further calculation, the product Ba which equals the interval area Kl multiplied by the integral median value of go is to be found. The integral median value of go equals the median integral value of rg multiplied by cos (alpha minus tau/2). Thereby it is possible to eliminate Kl as follows:

Ba Ale-g, AK,X F, cos(A 9/2) ITO/540M r )cos(a 6/2) The desired distance gc of the gravity or pressure center of the fluid containing pressure chamber or gc e of the pressure chamber from the axis of the rotor can now be found by calculating the integral over Ba divided by the integral median value over the intervals Kl, as follows:

' which leads to equations 7 and 8 for the inner and outer thrust chamber.

The very important final equation for finding the distance of the pressure center of the respective fluid containg pressure chamber or from the axis of the rotor or from the axis of the central portion(s) of the control body is not integrable without difficulties. It is however very convenient to calculate with it by calculating a number of intervalls Z of it and thereafter to divide and thus obtained sum by the number of intervals Z, as far as the value above the fraction line is concerned. Thereafter the thus obtained value is to be divided by the median value of K I, which was obtained by resorting to the equation (9). Thereby the value go of the location of the pressure center of the respective fluid containing pressure chamber or gc plus e is obtained with sufficient accuracy. I

I claim:

1. In a hydraulic or pneumatic aggregate, a combination comprising a housing having a socket; a channeled rotor mounted in said housing said having a face facing said socket; and a thrust member mounted in said socket and movable axially of said rotor, said member including a control portion having an annular control face adjacent to said face of said rotor, a first end face facing away from said control face, and a cylindrical peripheral surface, an eccentric second portion adjacent to said first end face and having a second end face facing away from said control portion and a second cylindrical peripheral surface, and a third portion adjacent to said second end face and having a third cylindri-' cal peripheral surface coaxial with said first peripheral surface, said peripheral surfaces sealingly engaging said housing and said member defining with said housing first and second annular pressure chambers respectively adjacent to said first and second end faces whereby the fluid in said chambers urges said control face toward said face of said rotor, said member further having first and second passages respectively extending between said control face and said first and second end faces, said control face having first and second pressure fluid zones having first and second centers and respectively including the corresponding ends of said first and second passages and said first and second faces respectively having third and fourthpressure fluid zones with third and fourth centers, the diameters of said peripheral surfaces, the eccentricity of said second position, the outer diameter of said control face and the configuration of said ends of said passages in said control face being such that the distance between the axis of said control portion and said first and second centers respectively equal or closely approximate the distances between the axis of said control portion and said third a d f tthsenterst V 2. A combination as defined in claim 1, wherein said first and third centers are located on a first line which is parallel to the axis of said control portion and said second and fourth centers are located on a second line which is parallel to the axis of said control portion.

3. A combination as defined in claim 2, wherein said first and second lines are located diametrically opposite each other with respect to the axis of said control portron.

4. A combination as defined in claim 2, wherein said face of said rotor is provided with a plurality of channels which seep along the ends of said first and second passages in said control face when said rotor relates to said thrust member.

5. A combination as defined in claim 4, wherein said rotor is provided with liquid displacing chambers communicating with said channels and further comprising liquid displacing elements movably mounted in said housing and extending into said liquid displacing chambers.

6. A combination as defined in claim 1, wherein the ends of said passages in said control face are disposed at a predetermined distance from the axis of said control portion.

7. A combination as defined in claim 1, wherein the diameter of said third peripheral surface is less than the diameter of said first or second peripheral surface and said control face is an angular face having a circular outer edge.

8. A combination as defined in claim 1, wherein said first peripheral surface has a first diameter and said control face has a second diameter, one of said first and second diameters being greater than the other thereof.

9. A combination as defined in claim 8, wherein said first diameter is greater than said second diameter.

10. A combination as defined in claim 1, wherein a portion of said second peripheral surface extends radi ally outwardly beyond said control face.

11. A combination as defined in claim 10, wherein said portion of said second peripheral surface is located radially inwardly of or is flush with said first peripheral surface.

12. A combination as defined in claim 1, wherein said housing comprises a one-piece portion which is provided with said socket.

13. A combination as defined in claim 1, wherein said end of at least one of said passages has an area exceeding the cross-sectional area of the remainder of said one passage.

14. A combination as defined in claim 13, wherein said end of said one passage extends beyond said remainder of said one passage as considered in the radial direction of said control portion. a

15. A combination as defined in claim 1, wherein th distance (Geo) between said first center and the axis of said control portion equals alphaJ/(alpha alpha wherein R is the radius of a circle slightly smaller than the radius of the outer edge of said control face and Ri is the radius of a circle slightly larger than the radius of the inner edge of said control face.

16. A combination as defined in claim 15, wherein the distance (goo) between said third center and the axis of said control portion equals or approximates 17. A combination as defined in claim 1, wherein the distance (Gci) between said second center and the axis of said control portion equals 601' 2(R0 Ri)/3(R0"" Ri) X (sin alpha sin alpha )/(alpha alpha,) 18. A combination as defined in claim 17, wherein the distance (gci) between said fourth center and the axis of said control portion equals or approximates 19. A combination as defined in claim 1, wherein the area of said first or second end face equals A X fb wherein fl) is less than 1.06 but more than 1.04 and ss: Ri) alpha pi/4 x 360.

20. A combination as defined in claim 1, wherein the area of saids first end face equals (r0 ri) pi/4 (R0 Ri alpha X pi/4 X 360 Xfb.

21. A combination as defined in claim 1, wherein the area of said second end face equals (rm ri pi/4 (R0 Ri alpha X pi/4 X 360 x fb.

22. A combination as defined in claim 1, wherein the outer diameter of said first pressure chamber exceeds the outer diameter of said control face.

23. A combination as defined in claim 1, wherein the diameter of said third peripheral surface exceeds the inner diameter of said control face.

24. A combination as defined in claim 1, wherein said control face is flat, at least in the regions surrounding said ends of said passages. v

25. A combination as defined in claim 1, wherein the distance between said ends of said passages and the inner and outer edges of said control face is l/5-l/20 inch.

26. A combination as defined in claim 1, wherein the cross-sectional area of each of said pressure chambers is 55-60 percent (plus minus 10 percent) of the effective area of said control face.

27. A combination as defined in claim 1, wherein said thrust member has an eccentric end portion whose eccentricity with respect to said controls portion is different from the eccentricity of said second portion.

28. A combination as defined in claim 1, wherein said thrust member consists of two parts including a front part which constitutes said control portion and a rear part which constitutes said second and third portions.

inner diameter of said control face.

mitten STATES PATENT oemen @ERTWECATE 0F QQRREQTWN PATENT NO. 3,850,201

DATED 3 Nov. 26, 1974 INVENTOR(S) I Karl Eickmann It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In column 16, line 21, cancel "said" (second occurrence) and substitute and In column 16, line 47, cancel "position" and. substitute portion *"a Signed and sealed this 15th day of July 1975.

(SEAL) Attest:

C2s MARSHALL DANN RUTH C, MASON Commissioner of Patents I i and Trademarks Attesting Officer 

1. In a hydraulic or pneumatic aggregate, a combination comprising a housing having a socket; a channeled rotor mounted in said housing and having a face facing said socket; and a thrust member mounted in said socket and movable axially of said rotor, said member including a control portion having an annular control face adjacent to said face of said rotor, a first end face facing away from said control face, and a cylindrical peripheral surface, an eccentric second portion adjacent to said first end face and having a second end face facing away from said control portion and a second cylindrical peripheral surface, and a third portion adjacent to said second end face and having a third cylindrical peripheral surface coaxial with said first peripheral surface, said peripheral surfaces sealingly engaging said housing and said member defining with said housing first and second annular pressure chambers respectively adjacent to said first and second end faces whereby the fluid in said chambers urges said control face toward said face of said rotor, said member further having first and second passages respectively extending between said control face and said first and second end faces, said control face having first and second pressure fluid zones having first and second centers and respectively including the corresponding ends of said first and second passages and said first and second faces respectively having third and fourth pressure fluid zones with third and fourth centers, the diameters of said peripheral surfaces, the eccentricity of said second position, the outer diameter of said control face and the configuration of said ends of said passages in said control face being such that the distances between the axis of said control portion and said first and second centers respectively equal or closely approximate the distances between the axis of said control portion and said third and fourth centers.
 2. A combination as defined in claim 1, wherein said first and third centers are located on a first line which is parallel to the axis of said control portion and said second and fourth centers are located on a second line which is parallel to the axis of said control portion.
 3. A combination as defined in claim 2, wherein said first and second lines are located diametrically opposite each other with respect to the axis of said control portion.
 4. A combination as defined in claim 2, wherein said face of said rotor is provided with a plurality of channels which seep along the ends of said first and second passages in said control face when said rotor relates to said thrust member.
 5. A combination as defined in claim 4, wherein said rotor is provided with liquid displacing chambers communicating with said channels and further comprising liquid displacing elements movably mounted in said housing and extending into said liquid displacing chambers.
 6. A combination as defined in claim 1, wherein the ends of said passages in said control face are disposed at a predetermined distance from the axis of said control portion.
 7. A combination as defined in claim 1, wherein the diameter of said third peripheral surface is less than the diameter of said first or second peripheral surface and said control face is an annular face having a circular outer edge.
 8. A combination as defined in claim 1, wherein said first peripheral surface has a first diameter and said control face has a second diameter, one of said first and second diameters being greater than the other thereof.
 9. A combination as defined in claim 8, wherein said first diameter is greater than said second diameter.
 10. A combination as defined in claim 1, wherein a portion of said second peripheral surface extends radially outwardly beyond said control face.
 11. A combination as defined in claim 10, wherein said portion of said second peripheral surface is located radially inwardly of or is flush with said first peripheral surface.
 12. A combination as defined in claim 1, wherein said housing comprises a one-piece portion which is provided with said socket.
 13. A combination as defined in claim 1, wherein said end of at least one of said passages has an area exceeding the cross-sectional area of the remainder of said one passage.
 14. A combination as defined in claim 13, wherein said end of said one passage extends beyond said remainder of said one passage as considered in the radial direction of said control portion.
 15. A combination as defined in claim 1, wherein the distance (Gco) between said first center and the axis of said control portion equals Gco 2(Ro3 -Ri3)/3 (Ro2 -Ri2) X (sin alpha2 -sin alpha1)/(alpha2 - alpha1) wherein Ro is the radius of a circle slightly smaller than the radius of the outer edge of said control face and Ri is the radius of a circle slightly larger than the radius of the inner edge of said control face.
 16. A combination as defined in claim 15, wherein the distance (gco) between said third center and the axis of said control portion equals or approximates
 17. A combination as defined in claim 1, wherein the distance (Gci) between said second center and the axis of said control portion equals Gci 2(Ro3 - Ri3)/3(Ro2 - Ri2) X (sin alpha2 -sin alpha1)/(alpha2 - alpha1)
 18. A combination as defined in claim 17, wherein the distance (gci) between said fourth center and the axis of said control portion equals or approximates
 19. A combination as defined in claim 1, wherein the area of said first or second end face equals AStz fb wherein fb is less than 1.06 but more than 1.04 and AStz (Ro2 - Ri2) alpha pi/4 X
 360. 20. A combination as defined in claim 1, wherein the area of said first end face equals (ro2 - ri2) pi/4 (Ro2 - Ri2) alpha X pi/4 X 360 X fb.
 21. A combination as defined in claim 1, wherein the area of said second end face equals (rm2 - ri2) pi/4 (Ro2 - Ri2) alpha X pi/4 X 360 x fb.
 22. A combination as defined in claim 1, wherein the outer diameter of said first pressure chamber exceeds the outer diameter of said control face.
 23. A combination as defined in claim 1, wherein the diameter of said third peripheral surface exceeds the inner diameter of said control face.
 24. A combination as defined in claim 1, wherein said control face is flat, at least in the regions surrounding said ends of said passages.
 25. A combination as defined in claim 1, wherein the distance between said ends of said pAssages and the inner and outer edges of said control face is 1/5-1/20 inch.
 26. A combination as defined in claim 1, wherein the cross-sectional area of each of said pressure chambers is 55-60 percent (plus minus 10 percent) of the effective area of said control face.
 27. A combination as defined in claim 1, wherein said thrust member has an eccentric end portion whose eccentricity with respect to said control portion is different from the eccentricity of said second portion.
 28. A combination as defined in claim 1, wherein said thrust member consists of two parts including a front part which constitutes said control portion and a rear part which constitutes said second and third portions.
 29. A combination as defined in claim 1, wherein said thrust member has at least one seat for at least one annular sealing element.
 30. A combination as defined in claim 1, wherein the diameter of said third peripheral surface exceeds the inner diameter of said control face. 